On-vehicle sound instruments such as car radios are often stolen on parking. Various improvements for preventing thefts have been made on the instruments.
One improvement is that a car radio comprising a main body and a face plate integrally fixed to the main body is detachably mounted on a vehicle-side mount. Such an improvement is superior in that the integral unit of instrument body and face plate can be removed and carried from the car and thus preventing potential thefts. It is however inferior in that the instrument body is relatively heavy.
Another improvement is that an on-vehicle sound instrument comprises a main instrument body fixedly mounted on a vehicle and only a face plate is detachable from the instrument body. The face plate includes various operation keys and indicators disposed on its front panel. Thus, the interior of the face plate includes switches activated by the operation keys, display such as liquid-crystal elements, lamps for providing operational indications and guidance to a user and other elements. These electronic/electric parts are mounted, for example, on a single circuit board. In addition, various connectors are disposed on the backside of the face plate, and are connected to the circuit board of the face plate. On the other hand, the instrument body fixedly mounted on the vehicle includes counterpart connectors which are to be electrically connected to the connectors of the face plate, respectively.
As for the latter instrument, the instrument body fixed on the vehicle cannot be started, if the face plate superior in portability is removed from the vehicle. Thus, the instrument body can be prevented from being stolen.
Since the prior art sound instrument with the detachable face plate includes the electronic/electric circuits and circuit board mounted on the side of the face plate, the connectors in the face plate must be connected to or disconnected from those of the instrument body, each time the face plate is mounted on or dismounted from the instrument body. The connectors are connected and disconnected so often as the driver gets on and off the vehicle, and it may result in poor connections. Moreover, the face plate is not necessarily always mounted on the instrument body in the proper orientation. In general, as for the face plate holding mechanisms of such a type, the face plate is mounted on or dismounted from the holder of the instrument body while rotating the face plate around a point at which the right side of the face plate engages the holder. This causes a relatively large load to the holes and pins in the male and female connectors, leading to further increase in poor connections mentioned above.
When the electronic/electric parts and circuit board are mounted on the face plate, an input section including various input switches as well as an output section including liquid-crystal displays and others are disposed on the face plate. This means that the instrument body is entirely separated from the input/output sections. Although such a structure can prevent potential thefts, it is very inconvenient for the manufacture of the on-vehicle sound instrument. This is because a performance test should be carried out in each manufacturing stage. Such a performance test can be made only when the face plate is actually mounted on the instrument body. This means that the face plate is frequently mounted on and dismounted from the instrument body throughout the manufacturing process.
The circuit board in the face plate must solely be subjected to its own performance test.
If the connectors are externally exposed from the face plate and instrument body, the following problems may be raised. When the portable face plate is solely carried or stored, the exposed pins, for example, in the face plate connectors may be damaged accidentally. In such a case, the sound instrument becomes unusable. Further, the exposed connectors may be broken intentionally by a thief.
Similarly, when the electronic/electric circuits and circuit board are mounted on the face plate, the following problems may be raised. The connectors in the face plate must be connected to or disconnected from those of the instrument body each time the face plate is mounted on or dismounted from the instrument body. Such connections and disconnections are repeated each time the driver gets on and off the vehicle. Further, the following problem is raised when the face plate is mounted on the instrument body.
A problem is raised when the driver turns OFF the ignition leaving the power of the car radio ON, and consecutively turns ON the ignition before mounting the face plate. In such a case, the instrument body may be started before all the terminals in the connectors of the instrument body and face plate are connected together. This is caused when the power switch terminals in the face plate are connected to the corresponding terminals in the instrument body before all the other terminals are completely connected to one another.
At this point, for example, a microcomputer in the instrument body is started immediately. A false signal other than normal signals may be input into the microcomputer since not all the terminals are connected. Thus, the microcomputer does not function properly even after all the terminals are in contact with one another. For example, even if the operation keys on the face plate are activated, the microcomputer does not operate at all. Further, the liquid-crystal display in the face plate is disturbed since it does not receive any normal drive signal.
Such a problem is raised when the face plate is not mounted on the instrument body in the proper orientation. This is because the connector terminals are sequentially connected to one another, starting from one end in the connector array. This problem tends to occur depending on the mounting mechanism in the face plate, for example, a mounting mechanism in which the face plate is mounted on or dismounted from the instrument body while rotating the face plate around a point where one side of the face plate is engaged with the instrument body.